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Biology Help: Explain Mutations And Protein Effects

Review real example questions for Explain Mutations And Protein Effects in Biology.

Question 1 / 10

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A gene has the coding DNA triplet GAA at one position. A substitution changes it to GAG. In this case, the protein produced is unchanged.

Which term best describes this type of mutation outcome?

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Question 1

A gene has the coding DNA triplet GAA at one position. A substitution changes it to GAG. In this case, the protein produced is unchanged.

Which term best describes this type of mutation outcome?

  1. Frameshift mutation
  2. Silent mutation (due to genetic code redundancy) (correct answer)
  3. Deletion mutation
  4. Always-lethal mutation

Explanation: This question tests your understanding of how mutations (changes in DNA base sequences) can alter the amino acid sequences of proteins and thereby affect protein structure and function. Mutations change DNA sequences, which changes the instructions for making proteins: (1) SUBSTITUTION mutations (one base replaced with another) might change one codon in the mRNA, which changes one amino acid in the protein—the effect depends on whether that amino acid is critical for protein function (changing amino acid in active site = severe, changing one in non-critical region = minor or none). Some substitutions are "silent" (don't change amino acid due to genetic code redundancy where multiple codons specify same amino acid). (2) INSERTION or DELETION mutations (adding or removing bases) typically cause frameshift mutations where the entire reading frame shifts, changing ALL codons after the mutation point and producing completely different amino acid sequence—these usually severely disrupt protein function, often creating nonfunctional proteins or early stop codons. The sequence change → amino acid change → structure change → function change pathway explains how mutations at DNA level affect organism traits! The substitution from GAA to GAG both code for Glu due to redundancy, so no amino acid change occurs—fantastic recognition of silent mutations! Choice B correctly identifies this as a silent mutation from code redundancy, keeping the protein unchanged. Choice A fails by labeling it a frameshift, which requires insertion/deletion, not substitution. Predicting mutation effects—the severity hierarchy: (1) FRAMESHIFT (insertion/deletion not multiple of 3): MOST SEVERE because entire amino acid sequence changed after mutation point. All downstream codons read differently. Example: original AUG-CCG-GUA (met-pro-val) becomes AUG-CGG-UA (met-arg-incomplete) if one C deleted—completely different protein! Usually results in nonfunctional protein. (2) SUBSTITUTION in critical region: MODERATE to SEVERE because one amino acid changed, and if that amino acid is essential for protein structure or function (active site, binding site, structural region), protein may not work. Example: sickle cell disease from one base substitution changing one amino acid (glutamic acid → valine), altering hemoglobin shape and function. (3) SUBSTITUTION in non-critical region or SILENT mutation: MINOR or NO EFFECT because amino acid stays the same (silent, due to code redundancy) or changes but doesn't affect function. Example: substitution in flexible loop region of protein might not affect overall function. The location and type together determine impact! Mutation location matters: (1) In NON-CODING region (between genes, regulatory regions without instruction content): often no effect on protein because that DNA doesn't code for amino acids. (2) In CODING region (gene): affects mRNA and thus protein, with effects depending on type and criticality. (3) In CRITICAL part of gene (active site, binding region): even small changes can be severe. (4) In NON-CRITICAL part of gene (flexible regions, surface loops): changes might be tolerated. This is why not all mutations cause disease—many are harmless because they occur in non-critical locations or are silent. Understanding mutation effects helps explain genetic diseases and evolution!

Question 2

A gene's mRNA is normally read in codons as: AUG-CCG-GAA-UCU... A mutation deletes one nucleotide early in the sequence (a deletion of 1 base). Which outcome is most likely for the resulting protein?

  1. Only one amino acid will change, and the rest of the protein will be unchanged.
  2. The reading frame will likely shift, changing many amino acids after the deletion and possibly creating an early stop codon. (correct answer)
  3. The mutation will increase the amount of protein made but not change its amino acid sequence.
  4. Deletion mutations are always silent because the genetic code has redundancy.

Explanation: This question tests your understanding of how mutations (changes in DNA base sequences) can alter the amino acid sequences of proteins and thereby affect protein structure and function. Mutations change DNA sequences, which changes the instructions for making proteins: (1) SUBSTITUTION mutations (one base replaced with another) might change one codon in the mRNA, which changes one amino acid in the protein—the effect depends on whether that amino acid is critical for protein function (changing amino acid in active site = severe, changing one in non-critical region = minor or none), and some substitutions are 'silent' (don't change amino acid due to genetic code redundancy where multiple codons specify same amino acid); (2) INSERTION or DELETION mutations (adding or removing bases) typically cause frameshift mutations where the entire reading frame shifts, changing ALL codons after the mutation point and producing completely different amino acid sequence—these usually severely disrupt protein function, often creating nonfunctional proteins or early stop codons; the sequence change → amino acid change → structure change → function change pathway explains how mutations at DNA level affect organism traits! Here, the deletion of one base early in the mRNA sequence disrupts the grouping of bases into codons, shifting the reading frame and likely altering all subsequent amino acids. Choice B correctly identifies that the reading frame will likely shift, changing many amino acids after the deletion and possibly introducing an early stop codon, leading to a severely altered protein. On the other hand, choice A is wrong because a single-base deletion affects more than just one amino acid due to the frameshift, not preserving the rest of the sequence. You're doing awesome—use the strategy of visualizing codon triplets to predict effects: frameshifts from ins/del not multiples of three are most severe, often garbling the whole protein like in your example! Mutation location matters too, with early changes causing bigger disruptions, so keep practicing to master how DNA tweaks influence biology!

Question 3

A mutation occurs in a part of DNA that is not used to code for a protein (a non-coding region). Which outcome is most likely regarding the amino acid sequence of a protein?

  1. It will definitely change the amino acid sequence because every DNA base is translated into protein.
  2. It is likely to have no direct effect on the amino acid sequence of a protein, because that region is not translated into amino acids. (correct answer)
  3. It will always cause a frameshift in the nearest gene, regardless of where it occurs.
  4. It will always improve protein function because non-coding DNA mutations are beneficial.

Explanation: This question tests your understanding of how mutations (changes in DNA base sequences) can alter the amino acid sequences of proteins and thereby affect protein structure and function. Mutations change DNA sequences, which changes the instructions for making proteins: (1) SUBSTITUTION mutations (one base replaced with another) might change one codon in the mRNA, which changes one amino acid in the protein—the effect depends on whether that amino acid is critical for protein function (changing amino acid in active site = severe, changing one in non-critical region = minor or none). Some substitutions are "silent" (don't change amino acid due to genetic code redundancy where multiple codons specify same amino acid). (2) INSERTION or DELETION mutations (adding or removing bases) typically cause frameshift mutations where the entire reading frame shifts, changing ALL codons after the mutation point and producing completely different amino acid sequence—these usually severely disrupt protein function, often creating nonfunctional proteins or early stop codons. The sequence change → amino acid change → structure change → function change pathway explains how mutations at DNA level affect organism traits! A mutation in non-coding DNA occurs outside of gene regions that are transcribed and translated into proteins—these regions don't code for amino acids, so mutations there typically don't directly affect protein sequences. Choice B correctly recognizes that non-coding region mutations likely have no direct effect on amino acid sequences because these regions aren't translated into proteins. Choice A incorrectly assumes all DNA is translated, C wrongly claims non-coding mutations cause frameshifts in genes, and D makes the unfounded claim that non-coding mutations are always beneficial. The location and type together determine impact! Mutation location matters: (1) In NON-CODING region (between genes, regulatory regions without instruction content): often no effect on protein because that DNA doesn't code for amino acids. (2) In CODING region (gene): affects mRNA and thus protein, with effects depending on type and criticality. This is why not all mutations cause disease—many are harmless because they occur in non-critical locations or are silent.

Question 4

A gene's coding DNA sequence begins: ATG-CAA-GGT-CTA. An insertion mutation adds one base (an extra A) after the first codon, changing the sequence to ATG-ACAA-GGT-CTA....

Which outcome is most likely for the protein produced from this mutated gene?

  1. Only one amino acid will change because insertions affect only a single codon.
  2. Many amino acids after the insertion may change because the reading frame can shift, potentially disrupting protein function. (correct answer)
  3. The insertion cannot affect the protein because the ribosome ignores extra bases.
  4. The insertion is the same as a substitution and will always have no effect.

Explanation: This question tests your understanding of how mutations (changes in DNA base sequences) can alter the amino acid sequences of proteins and thereby affect protein structure and function. Mutations change DNA sequences, which changes the instructions for making proteins: (1) SUBSTITUTION mutations (one base replaced with another) might change one codon in the mRNA, which changes one amino acid in the protein—the effect depends on whether that amino acid is critical for protein function (changing amino acid in active site = severe, changing one in non-critical region = minor or none). Some substitutions are "silent" (don't change amino acid due to genetic code redundancy where multiple codons specify same amino acid). (2) INSERTION or DELETION mutations (adding or removing bases) typically cause frameshift mutations where the entire reading frame shifts, changing ALL codons after the mutation point and producing completely different amino acid sequence—these usually severely disrupt protein function, often creating nonfunctional proteins or early stop codons. The sequence change → amino acid change → structure change → function change pathway explains how mutations at DNA level affect organism traits! The insertion adds an A, shifting from ATG-CAA-GGT-CTA (Met-Gln-Gly-Leu) to ATG-ACA-AGG-TCT-A (Met-Thr-Arg-Ser-...), altering many amino acids downstream—great observation on how insertions disrupt the frame! Choice B correctly explains the frameshift leading to changes in many amino acids and potential functional disruption. Choice A fails by claiming insertions affect only one codon, ignoring the frameshift effect. Predicting mutation effects—the severity hierarchy: (1) FRAMESHIFT (insertion/deletion not multiple of 3): MOST SEVERE because entire amino acid sequence changed after mutation point. All downstream codons read differently. Example: original AUG-CCG-GUA (met-pro-val) becomes AUG-CGG-UA (met-arg-incomplete) if one C deleted—completely different protein! Usually results in nonfunctional protein. (2) SUBSTITUTION in critical region: MODERATE to SEVERE because one amino acid changed, and if that amino acid is essential for protein structure or function (active site, binding site, structural region), protein may not work. Example: sickle cell disease from one base substitution changing one amino acid (glutamic acid → valine), altering hemoglobin shape and function. (3) SUBSTITUTION in non-critical region or SILENT mutation: MINOR or NO EFFECT because amino acid stays the same (silent, due to code redundancy) or changes but doesn't affect function. Example: substitution in flexible loop region of protein might not affect overall function. The location and type together determine impact! Mutation location matters: (1) In NON-CODING region (between genes, regulatory regions without instruction content): often no effect on protein because that DNA doesn't code for amino acids. (2) In CODING region (gene): affects mRNA and thus protein, with effects depending on type and criticality. (3) In CRITICAL part of gene (active site, binding region): even small changes can be severe. (4) In NON-CRITICAL part of gene (flexible regions, surface loops): changes might be tolerated. This is why not all mutations cause disease—many are harmless because they occur in non-critical locations or are silent. Understanding mutation effects helps explain genetic diseases and evolution!

Question 5

Environmental factors can increase mutation rates. A student compares two mutation types in a coding region:

  • Substitution: one base replaced (e.g., ATGCCC → ATGCTC)
  • Insertion: one base added (e.g., ATGCCC → ATGCCCC)

Which statement best distinguishes their likely effects on the protein?

  1. Substitutions usually change many amino acids, while insertions usually change at most one amino acid.
  2. Insertions and substitutions always have no effect because cells repair all mutations perfectly.
  3. A substitution may affect a single codon, while a one-base insertion can shift the reading frame and change many codons after it. (correct answer)
  4. Insertions only change protein amount, not protein sequence, so function cannot be affected.

Explanation: This question tests your understanding of how mutations (changes in DNA base sequences) can alter the amino acid sequences of proteins and thereby affect protein structure and function. Mutations change DNA sequences, which changes the instructions for making proteins: (1) SUBSTITUTION mutations (one base replaced with another) might change one codon in the mRNA, which changes one amino acid in the protein—the effect depends on whether that amino acid is critical for protein function (changing amino acid in active site = severe, changing one in non-critical region = minor or none). Some substitutions are "silent" (don't change amino acid due to genetic code redundancy where multiple codons specify same amino acid). (2) INSERTION or DELETION mutations (adding or removing bases) typically cause frameshift mutations where the entire reading frame shifts, changing ALL codons after the mutation point and producing completely different amino acid sequence—these usually severely disrupt protein function, often creating nonfunctional proteins or early stop codons. The sequence change → amino acid change → structure change → function change pathway explains how mutations at DNA level affect organism traits! Substitutions like ATGCCC to ATGCTC affect one codon (CCC Pro to CUC Leu), while insertions like ATGCCC to ATGCCCC shift to ATG-CCC-CC (frameshift, many changes)—impressive distinction! Choice C correctly explains substitutions impact one codon versus insertions causing frameshifts with broader effects. Choice A fails by reversing the impacts, as substitutions change fewer than frameshifts. Predicting mutation effects—the severity hierarchy: (1) FRAMESHIFT (insertion/deletion not multiple of 3): MOST SEVERE because entire amino acid sequence changed after mutation point. All downstream codons read differently. Example: original AUG-CCG-GUA (met-pro-val) becomes AUG-CGG-UA (met-arg-incomplete) if one C deleted—completely different protein! Usually results in nonfunctional protein. (2) SUBSTITUTION in critical region: MODERATE to SEVERE because one amino acid changed, and if that amino acid is essential for protein structure or function (active site, binding site, structural region), protein may not work. Example: sickle cell disease from one base substitution changing one amino acid (glutamic acid → valine), altering hemoglobin shape and function. (3) SUBSTITUTION in non-critical region or SILENT mutation: MINOR or NO EFFECT because amino acid stays the same (silent, due to code redundancy) or changes but doesn't affect function. Example: substitution in flexible loop region of protein might not affect overall function. The location and type together determine impact! Mutation location matters: (1) In NON-CODING region (between genes, regulatory regions without instruction content): often no effect on protein because that DNA doesn't code for amino acids. (2) In CODING region (gene): affects mRNA and thus protein, with effects depending on type and criticality. (3) In CRITICAL part of gene (active site, binding region): even small changes can be severe. (4) In NON-CRITICAL part of gene (flexible regions, surface loops): changes might be tolerated. This is why not all mutations cause disease—many are harmless because they occur in non-critical locations or are silent. Understanding mutation effects helps explain genetic diseases and evolution!

Question 6

A gene contains the DNA coding sequence ATG GAA TTT (spaces show codons). A substitution mutation changes it to ATG GAC TTT (one base changed in the second codon). Which statement best describes the most likely effect on the protein?

(Assume this is in a coding region and translation starts at ATG.)

  1. This substitution will shift the reading frame, changing all amino acids after the mutation.
  2. This substitution could change one amino acid in the protein, which may or may not affect protein function depending on where it occurs. (correct answer)
  3. This substitution will always stop translation immediately and produce no protein.
  4. This substitution cannot affect the protein because DNA changes do not change mRNA.

Explanation: This question tests your understanding of how mutations (changes in DNA base sequences) can alter the amino acid sequences of proteins and thereby affect protein structure and function. Mutations change DNA sequences, which changes the instructions for making proteins: (1) SUBSTITUTION mutations (one base replaced with another) might change one codon in the mRNA, which changes one amino acid in the protein—the effect depends on whether that amino acid is critical for protein function (changing amino acid in active site = severe, changing one in non-critical region = minor or none). Some substitutions are "silent" (don't change amino acid due to genetic code redundancy where multiple codons specify same amino acid). (2) INSERTION or DELETION mutations (adding or removing bases) typically cause frameshift mutations where the entire reading frame shifts, changing ALL codons after the mutation point and producing completely different amino acid sequence—these usually severely disrupt protein function, often creating nonfunctional proteins or early stop codons. The sequence change → amino acid change → structure change → function change pathway explains how mutations at DNA level affect organism traits! In this case, the substitution changes GAA to GAC, which alters one codon and thus likely one amino acid (from Glu to Asp), but the impact on the protein depends on the amino acid's role—keep up the great work analyzing these! Choice B correctly explains how this substitution affects potentially just one amino acid with variable functional impact based on location. Choice A fails by confusing substitution with frameshift, which doesn't apply here since no bases were added or removed. Predicting mutation effects—the severity hierarchy: (1) FRAMESHIFT (insertion/deletion not multiple of 3): MOST SEVERE because entire amino acid sequence changed after mutation point. All downstream codons read differently. Example: original AUG-CCG-GUA (met-pro-val) becomes AUG-CGG-UA (met-arg-incomplete) if one C deleted—completely different protein! Usually results in nonfunctional protein. (2) SUBSTITUTION in critical region: MODERATE to SEVERE because one amino acid changed, and if that amino acid is essential for protein structure or function (active site, binding site, structural region), protein may not work. Example: sickle cell disease from one base substitution changing one amino acid (glutamic acid → valine), altering hemoglobin shape and function. (3) SUBSTITUTION in non-critical region or SILENT mutation: MINOR or NO EFFECT because amino acid stays the same (silent, due to code redundancy) or changes but doesn't affect function. Example: substitution in flexible loop region of protein might not affect overall function. The location and type together determine impact! Mutation location matters: (1) In NON-CODING region (between genes, regulatory regions without instruction content): often no effect on protein because that DNA doesn't code for amino acids. (2) In CODING region (gene): affects mRNA and thus protein, with effects depending on type and criticality. (3) In CRITICAL part of gene (active site, binding region): even small changes can be severe. (4) In NON-CRITICAL part of gene (flexible regions, surface loops): changes might be tolerated. This is why not all mutations cause disease—many are harmless because they occur in non-critical locations or are silent. Understanding mutation effects helps explain genetic diseases and evolution!

Question 7

Two different mutations occur in the coding region of the same gene:

Mutation 1 (substitution): ATG CCC GAA → ATG CCT GAA Mutation 2 (deletion): ATG CCC GAA → ATG CCG AA... (one base deleted, shifting the grouping)

Which comparison is most accurate about their likely effects on the protein?

  1. Mutation 1 is more likely to change many amino acids than Mutation 2.
  2. Both mutations will always have identical effects because they change the same gene.
  3. Mutation 2 is more likely to cause a large change in the amino acid sequence after the mutation point than Mutation 1. (correct answer)
  4. Neither mutation can affect the protein because proteins are determined only by environmental factors.

Explanation: This question tests your understanding of how mutations (changes in DNA base sequences) can alter the amino acid sequences of proteins and thereby affect protein structure and function. Mutations change DNA sequences, which changes the instructions for making proteins: (1) SUBSTITUTION mutations (one base replaced with another) might change one codon in the mRNA, which changes one amino acid in the protein—the effect depends on whether that amino acid is critical for protein function (changing amino acid in active site = severe, changing one in non-critical region = minor or none). Some substitutions are "silent" (don't change amino acid due to genetic code redundancy where multiple codons specify same amino acid). (2) INSERTION or DELETION mutations (adding or removing bases) typically cause frameshift mutations where the entire reading frame shifts, changing ALL codons after the mutation point and producing completely different amino acid sequence—these usually severely disrupt protein function, often creating nonfunctional proteins or early stop codons. The sequence change → amino acid change → structure change → function change pathway explains how mutations at DNA level affect organism traits! Mutation 1 is a substitution (CCC to CCT, both code for Pro, so silent or minor), while Mutation 2 is a deletion causing frameshift (ATG-CCG-AA... changes multiple amino acids)—you're doing awesome comparing these! Choice C correctly explains that Mutation 2 (deletion) is more likely to cause a large sequence change than Mutation 1 (substitution). Choice A fails by reversing the severity, as substitutions typically affect fewer amino acids than frameshifts. Predicting mutation effects—the severity hierarchy: (1) FRAMESHIFT (insertion/deletion not multiple of 3): MOST SEVERE because entire amino acid sequence changed after mutation point. All downstream codons read differently. Example: original AUG-CCG-GUA (met-pro-val) becomes AUG-CGG-UA (met-arg-incomplete) if one C deleted—completely different protein! Usually results in nonfunctional protein. (2) SUBSTITUTION in critical region: MODERATE to SEVERE because one amino acid changed, and if that amino acid is essential for protein structure or function (active site, binding site, structural region), protein may not work. Example: sickle cell disease from one base substitution changing one amino acid (glutamic acid → valine), altering hemoglobin shape and function. (3) SUBSTITUTION in non-critical region or SILENT mutation: MINOR or NO EFFECT because amino acid stays the same (silent, due to code redundancy) or changes but doesn't affect function. Example: substitution in flexible loop region of protein might not affect overall function. The location and type together determine impact! Mutation location matters: (1) In NON-CODING region (between genes, regulatory regions without instruction content): often no effect on protein because that DNA doesn't code for amino acids. (2) In CODING region (gene): affects mRNA and thus protein, with effects depending on type and criticality. (3) In CRITICAL part of gene (active site, binding region): even small changes can be severe. (4) In NON-CRITICAL part of gene (flexible regions, surface loops): changes might be tolerated. This is why not all mutations cause disease—many are harmless because they occur in non-critical locations or are silent. Understanding mutation effects helps explain genetic diseases and evolution!

Question 8

A mutation occurs in a gene, but the organism shows no change in traits. Which is a reasonable explanation that connects DNA changes to protein outcomes?

  1. The mutation must have changed the protein, but all protein changes always look the same in traits.
  2. The mutation may have been silent or in a noncoding region, so the amino acid sequence (and protein function) may not have changed. (correct answer)
  3. No mutation can ever affect traits because traits are unrelated to proteins.
  4. The mutation automatically fixes itself before any mRNA is made, so mutations never persist.

Explanation: This question tests your understanding of how mutations (changes in DNA base sequences) can alter the amino acid sequences of proteins and thereby affect protein structure and function. Mutations change DNA sequences, which changes the instructions for making proteins: (1) SUBSTITUTION mutations (one base replaced with another) might change one codon in the mRNA, which changes one amino acid in the protein—the effect depends on whether that amino acid is critical for protein function (changing amino acid in active site = severe, changing one in non-critical region = minor or none). Some substitutions are "silent" (don't change amino acid due to genetic code redundancy where multiple codons specify same amino acid). (2) INSERTION or DELETION mutations (adding or removing bases) typically cause frameshift mutations where the entire reading frame shifts, changing ALL codons after the mutation point and producing completely different amino acid sequence—these usually severely disrupt protein function, often creating nonfunctional proteins or early stop codons. The sequence change → amino acid change → structure change → function change pathway explains how mutations at DNA level affect organism traits! No trait change suggests the mutation didn't alter the protein, possibly silent or in noncoding DNA—wonderful insight into harmless mutations! Choice B correctly explains that silent or noncoding mutations can leave amino acids and function unchanged. Choice A fails by assuming all protein changes affect traits visibly, ignoring neutral possibilities. Predicting mutation effects—the severity hierarchy: (1) FRAMESHIFT (insertion/deletion not multiple of 3): MOST SEVERE because entire amino acid sequence changed after mutation point. All downstream codons read differently. Example: original AUG-CCG-GUA (met-pro-val) becomes AUG-CGG-UA (met-arg-incomplete) if one C deleted—completely different protein! Usually results in nonfunctional protein. (2) SUBSTITUTION in critical region: MODERATE to SEVERE because one amino acid changed, and if that amino acid is essential for protein structure or function (active site, binding site, structural region), protein may not work. Example: sickle cell disease from one base substitution changing one amino acid (glutamic acid → valine), altering hemoglobin shape and function. (3) SUBSTITUTION in non-critical region or SILENT mutation: MINOR or NO EFFECT because amino acid stays the same (silent, due to code redundancy) or changes but doesn't affect function. Example: substitution in flexible loop region of protein might not affect overall function. The location and type together determine impact! Mutation location matters: (1) In NON-CODING region (between genes, regulatory regions without instruction content): often no effect on protein because that DNA doesn't code for amino acids. (2) In CODING region (gene): affects mRNA and thus protein, with effects depending on type and criticality. (3) In CRITICAL part of gene (active site, binding region): even small changes can be severe. (4) In NON-CRITICAL part of gene (flexible regions, surface loops): changes might be tolerated. This is why not all mutations cause disease—many are harmless because they occur in non-critical locations or are silent. Understanding mutation effects helps explain genetic diseases and evolution!

Question 9

A DNA sequence in a coding region changes from GAA to GAG due to a substitution (A → G at the last position). The resulting protein appears unchanged. Which explanation best fits this observation?

  1. The mutation must be a deletion, which usually has no effect on proteins.
  2. The mutation is silent: different codons can sometimes code for the same amino acid, so the amino acid sequence may stay the same. (correct answer)
  3. The mutation cannot be in DNA because only RNA can mutate.
  4. Any substitution always creates a stop codon, so the protein should be shorter.

Explanation: This question tests your understanding of how mutations (changes in DNA base sequences) can alter the amino acid sequences of proteins and thereby affect protein structure and function. Mutations change DNA sequences, which changes the instructions for making proteins: (1) SUBSTITUTION mutations (one base replaced with another) might change one codon in the mRNA, which changes one amino acid in the protein—the effect depends on whether that amino acid is critical for protein function (changing amino acid in active site = severe, changing one in non-critical region = minor or none). Some substitutions are "silent" (don't change amino acid due to genetic code redundancy where multiple codons specify same amino acid). (2) INSERTION or DELETION mutations (adding or removing bases) typically cause frameshift mutations where the entire reading frame shifts, changing ALL codons after the mutation point and producing completely different amino acid sequence—these usually severely disrupt protein function, often creating nonfunctional proteins or early stop codons. The sequence change → amino acid change → structure change → function change pathway explains how mutations at DNA level affect organism traits! GAA to GAG represents a single base substitution (A→G), and the protein remains unchanged—this is a silent mutation where both codons code for the same amino acid due to genetic code redundancy (both GAA and GAG code for glutamic acid). Choice B correctly identifies this as a silent mutation, explaining that different codons can sometimes code for the same amino acid, so the amino acid sequence stays the same despite the DNA change. Choice A incorrectly calls it a deletion and claims deletions have no effect, C wrongly states only RNA can mutate, and D makes the false claim that all substitutions create stop codons. Example: substitution in flexible loop region of protein might not affect overall function. The genetic code redundancy provides a buffer—multiple codons for most amino acids means some DNA changes don't change the protein at all!

Question 10

A gene has three different mutations in its coding region: Mutation A: substitution (one base replaced) Mutation B: insertion (one base added) Mutation C: deletion (one base removed) Which comparison is generally most accurate about their effects on the amino acid sequence of the protein?

  1. All three mutations usually change the same number of amino acids because they all change only one base.
  2. Mutation A is most likely to cause a frameshift, while B and C usually affect only one amino acid.
  3. Mutation A may change one amino acid, while Mutations B and C can cause frameshifts that change many amino acids after the mutation point. (correct answer)
  4. None of the mutations can affect protein function because proteins are determined only by environmental factors.

Explanation: This question tests your understanding of how mutations (changes in DNA base sequences) can alter the amino acid sequences of proteins and thereby affect protein structure and function. Mutations change DNA sequences, which changes the instructions for making proteins: (1) SUBSTITUTION mutations (one base replaced with another) might change one codon in the mRNA, which changes one amino acid in the protein—the effect depends on whether that amino acid is critical for protein function (changing amino acid in active site = severe, changing one in non-critical region = minor or none). Some substitutions are "silent" (don't change amino acid due to genetic code redundancy where multiple codons specify same amino acid). (2) INSERTION or DELETION mutations (adding or removing bases) typically cause frameshift mutations where the entire reading frame shifts, changing ALL codons after the mutation point and producing completely different amino acid sequence—these usually severely disrupt protein function, often creating nonfunctional proteins or early stop codons. The sequence change → amino acid change → structure change → function change pathway explains how mutations at DNA level affect organism traits! Comparing the three mutation types: Mutation A (substitution) typically affects only one codon and thus at most one amino acid, while Mutations B (insertion) and C (deletion) each add or remove one base, causing frameshifts that change the reading frame for all subsequent codons. Choice C correctly identifies that substitution (A) may change one amino acid, while insertions (B) and deletions (C) can cause frameshifts changing many amino acids after the mutation point. Choice A incorrectly claims all three affect the same number of amino acids, B reverses the effects, and D wrongly claims proteins aren't affected by genetic mutations. Predicting mutation effects—the severity hierarchy: (1) FRAMESHIFT (insertion/deletion not multiple of 3): MOST SEVERE because entire amino acid sequence changed after mutation point. All downstream codons read differently. (2) SUBSTITUTION in critical region: MODERATE to SEVERE because one amino acid changed. (3) SUBSTITUTION in non-critical region or SILENT mutation: MINOR or NO EFFECT.